Synthesis, characterization and catalytic activity of a mononuclear nonheme copper(II)-iodosylbenzene adduct

Iodosylbenzene (PhIO) and its derivatives have attracted significant attention due to their various applications in organic synthesis and biomimetic studies. For example, PhIO has been extensively used for generating high-valent metal-oxo species that have been regarded as key intermediates in diverse oxidative reactions in biological system. However, recent studies have shown that metal-iodosylbenzene adduct, known as a precursor of metal-oxo species, plays an important role in transition metal-catalyzed oxidation reactions. During last few decades, extensive investigations have been conducted on the synthesis and reactivity studies of metal-iodosylbenzene adducts with early and middle transition metals including manganese, iron, cobalt. Nevertheless, metal-iodosylbenzene adducts with late transition metals such as nickel, copper and zinc, still remains elusive. Herein, we report a novel copper(II)-iodosylbenzene adduct bearing a linear ligand composed of two pyridine rings and an ethoxyethanol side-chain, [Cu(OIPh)(HN₃O₂)]²⁺ (1). The copper(II)-iodosylbenzene adduct was characterized by several spectroscopic methods including UV-vis spectroscopy, electrospray ionization mass spectrometer (ESI MS), and electron paramagnetic resonance (EPR) combined with theoretical calculations. Interestingly, 1 can carry out the catalytic sulfoxidation reaction. In sulfoxidation reaction with thioanisole under catalytic reaction condition, not only two-electron but also four-electron oxidized products such sulfoxide and sulfone were yielded, respectively. However, 1 was not an efficient oxidant towards CH bond activation and epoxidation reactions due to the steric hindrance created by the intramolecular H-bonding interaction between HN₃O₂ ligand and iodosylbenzene moiety.